The present invention relates to a pneumatic tire reinforced with high modulus cords which is suitable for use on an aircraft.
It is generally recognized in the tire art that tires suitable for use on aircraft must be capable of operating under conditions of very high speeds and large loads as compared to tires used on automobiles, busses, trucks or similar earthbound vehicles. Tires used on earthbound vehicles undergo millions of flexes (rotations) during their lifetime under loads that fall in a relatively small range. Aircraft tires are subjected to high centrifugal forces and large loads on takeoff and high sudden impact stresses (including a high G-force) and loads during landing. An aircraft tire undergoes relatively few flexes (compared to earthbound tires) during its lifetime. As used herein and in the claims, a tire is xe2x80x9csuitable for use on an aircraftxe2x80x9d if the tire is of a size and load range, or ply rating, specified in either the xe2x80x9cYearbook of the Tire and Rim Associationxe2x80x9d, or the xe2x80x9cYearbook of the European Tyre and Rim Technical Organization,xe2x80x9d or in the current U.S.A. military specification xe2x80x9cMIL-T-5041xe2x80x9d. In the prior-art, in order to meet the required ratings, aircraft tires were made using a large number of carcass plies and breaker plies having a high e.p.i. count of multifilament cords, usually nylon, as reinforcement. Nylon is a preferred reinforcement material for aircraft tires since it is fatigue resistant and is otherwise more forgiving than other types of reinforcement materials, and is compatible with the high heat tolerant rubber compounds needed for use in aircraft tires. Nylon reinforcement materials, however, melt at a relatively low temperature and soften at normal aircraft tire operating temperatures, which makes a tire made with nylon reinforcement subject to flatspotting. Also, it is because nylon does not have the strength of other types of reinforcement materials that the large number of plies discussed above are needed to build aircraft tires.
Although higher modulus materials that melt at a higher temperature than nylon, such as polyesters, would make a tire more resistant to flatspotting, and possibly lighter weight, high modulus materials have not been generally considered to be broadly useful reinforcement material in aircraft tires since they appear to have low compatibility with the high temperature stable rubber compounds that are most frequently used in aircraft tires.
The present invention relates to a pneumatic tire suitable for use on an aircraft. The tire comprises (a) at least a pair of axially spaced substantially inextensible beads, (b) carcass plies wrapped over the beads, (c) breaker plies disposed radially outward of the carcass plies in a crown portion of the tire. The carcass plies and the breaker plies comprise substantially parallel high modulus cords imbedded in a rubber compound having the formula
wherein ingredients are listed in parts by weight per hundred parts by weight rubber, and the compound contains no free amines. Promoters for the rubber compound are selected from the group consisting of resorcinol, hexamethylenetetramine, hexamethoxymethylmelamine and reactive phenol-formaldehyde resin and the accelerator may be non-amine generating and is selected from the group consisting of sulfenamide accelerators or benzothiazole accelerators. The high modulus cords have a tenacity of 6.6 to 8.2 g/denier, an initial modulus of 120 to is 280 g/denier, an elongation at break of 8 to 18% and a shrinkage of not greater than 3% . The high modulus cords of the breaker plies are embedded in the rubber compound at an end count of 6 to 28 e.p.i.
In accordance with this invention, it has been found that compounds having a 300% modulus of 12-18 MPa and a minimum tensile strength of 23 MPa as tested per ASTM D412, and a T90 of between 30 and 40 minutes at a reference temperature of 135 degrees C. as tested per ASTM D2084 are suitable for use in this invention.
As used herein and in the claims, the terms
xe2x80x9caxialxe2x80x9d and xe2x80x9caxiallyxe2x80x9d refer to directions which are parallel to the axis of rotation of a tire,
xe2x80x9cradialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d refer to directions that are perpendicular to the axis of rotation of a tire,
xe2x80x9cbeadxe2x80x9d refers to that part of a tire comprising an annular tensile member wrapped by ply cords and shaped, with or without other reinforcement elements to fit a designed tire rim,
xe2x80x9capexxe2x80x9d refers to a wedge of elastomeric material placed beside (radially above the bead) the bead which supports the bead area and minimizes flexing in the bead area,
xe2x80x9ccarcassxe2x80x9d refers to the tire structure apart from the belt structure, tread, undertread, and sidewall rubber but including the beads, (carcass plies are wrapped around the beads),
xe2x80x9cflipperxe2x80x9d refers to additional reinforcement (usually fabric) that is placed around the bead/apex and, usually, between the bead/apex and the carcass ply,
xe2x80x9cequatorial planexe2x80x9d refers to a plane that is perpendicular to the axis of rotation of a tire and passes through the center of the tire""s tread,
xe2x80x9cbreaker pliesxe2x80x9d refers to annular reinforcement members in the crown area of the tire having longitudinal reinforcement members having an angle (in the illustrated embodiment) with respect to the equatorial plane of the tire of about 50xc2x0 less than the angle of such reinforcement members in the (bias) carcass plies,
xe2x80x9ccrownxe2x80x9d refers to substantially the outer circumference of a tire where the tread is disposed,
xe2x80x9ctenacityxe2x80x9d refers to stress expressed as force per unit linear density of an unstrained specimen (gm/tex or gm/denier), (usually used in textiles), and
xe2x80x9cmodulusxe2x80x9d refers to the ratio of the change in stress to the change in strain.